Atmospheric Chemistry and Physics, vol. 13, issue 22 (2013) pp. 11391-11401
The significance of ion-ion recombination for atmospheric new particle
formation is not well quantified. Here we present and evaluate a method
for determining the size distribution of recombination products from the
size distributions of neutral and charged clusters. Our method takes
into account the production of recombination products in the collisions
between oppositely charged ions and the loss due to coagulation.
Furthermore, unlike previous studies, we also consider the effect of
condensational growth on the size distribution of recombination
products. We applied our method to the data measured in Hyytiala,
Finland, to estimate the contribution of ion-ion recombination to the
concentrations of atmospheric clusters in the size range of 0.9-2.1 nm.
We observed that the concentration of recombination products was highest
in the size classes between 1.5 and 1.9 nm. The median concentrations of
recombination products were between 6 and 69 cm(-3) in different size
classes, which resulted in a small proportion of all neutral clusters,
varying between 0.2 and 13 %. When examining the whole size range
between 0.9 and 2.1 nm, the median fraction of recombination products of
all neutral clusters was only 1.5 %. We also investigated how the
results change if the effect of condensational growth is neglected. It
seems that with that assumption the fragmentation of newly formed
recombination products has to be taken into account, or else the
concentration of recombination products is overestimated. Overall, we
concluded that our method provides reasonable results, which are
consistent with the earlier estimates on the contribution of
recombination products to atmospheric cluster population in Hyytiala.
Still, in order to determine the size distribution of recombination
products more accurately in the future, more precise measurements of the
size distribution of atmospheric clusters would be needed.
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